The Jet Effect

Electric ducted fan-equipped airframe breaks speed record, establishing new flight path for commercial UAV innovation.

by Vicki Speed, Technology Reporter, Inside Unmanned Systems

Innovation in the aeromodelling space may not seem like the forum for advancement in commercial and military UAV operations—or is it?

In 2019, one of the world’s most successful high-speed aeromodelling pilots, Bruno Stükerjürgen, wanted to compete in one of the field’s biggest speed challenge events in Osnabrück, Germany. Stükerjürgen’s goal was to build a custom airframe, instead of using the conventional slim design, that could exceed the seemingly unreachable 400 kph record for model airplane flight speed.

To achieve his goal, he sought the expertise of fellow aeromodeller Daniel Schubeler, founder of Schubeler Technologies GmbH, a premier German manufacturer of advanced fan propulsion systems and lightweight composite parts which is part of commercial UAV developer, Microdrones.

Schubeler recommended an electric-powered ducted fan, or EDF-enabled propulsion system, similar to the systems used in airships and aircraft, to deliver higher air speeds. The result far exceeded Stükerjürgen’s expectations and opened the door for the development of a new generation of unmanned commercial and military systems where safety and speed counts.

Optimized for Speed

Stükerjürgen’s airframe was designed by a student from the RWTH Aachen University, a research university located in that North Rhine-Westphalia, Germany, city.

Stükerjürgen provided airframe flight parameters such as drag coefficients to Schubeler Technologies to design the ducted fan. Whether robust turbo fans, compressors or electric motors, Schubeler products are designed to withstand extreme conditions and demanding field use, and to provide thrust power and lightweight durability to high-tech applications including UAVs, professional motorsports and heavy-duty outdoor equipment.

A ducted fan is a shrouded low-diameter axial fan, ideal for generating higher pressure, lower-volume flow and high-exhaust speed. Unlike an exposed propeller, ducted fans, also known as axial fans, feature blades that are mounted inside a cowling. This design is critical to making the blades efficient (i.e., high thrust, low power). Even the smallest error in an aerodynamic system can cause a loss of 30 to 40 percent efficiency.

Schubeler believed the electric ducted fan solution would be easier to build than conventional electric propulsion or multi-engine solutions and deliver higher maneuverability.

For Stükerjürgen’s airframe, Schubeler worked with dynamic performance curves—available for every Schubeler ducted fan—to predict power consumption at different speeds. The team also designed the inlet and outlet geometries, crucial characteristics for any optimized system. The blade design was also critical for delivering a safe and reliable system that yields high thrust with low power input and longer flight times. Early estimates showed the DS-51-AXI HDS (90 mm) with a standard motor would achieve at least 430 kph while consuming less than 6kW.

Stükerjürgen and Schubeler put the concept to the test a few months later at the Osnabrück aeromodelling competition.

Stükerjürgen’s airframe, launched from a catapult, achieved a top speed of 460 kph and a steady state speed of 430 kph in the track—all while using around 500W less input than other systems.

Schubeler said, “The system is fast, powerful and highly efficient. We achieved an efficiency of around 65 percent, which is comparable to fast-spinning propellers for higher speeds.” He is especially proud that the reality closely matched the theoretical numbers, adding, “Our real-world results aligned with our predictions about power and speed in the first approach.

We didn’t need multiple design loops—that’s very satisfying.”

EDF in the Extreme

While the Stükerjürgen project was a fun and highly successful experiment to demonstrate that an electric ducted fan could power a high-speed hobby airframe, it has proven to be much more significant in the UAV space.

“Fundamentally, we were able to prove that fan propulsion systems are an efficient alternative to propellers, if integrated well,” Schubeler explained. “An electric ducted fan propulsion system offers more affordable power options for unmanned aircraft as compared to small jet engine-enabled systems.”

Conventional thought is that to increase the thrust of an electric ducted fan, thus delivering more power and speed, requires additional weight. However, the Schubeler development team is able to match duct fan systems—including optimal pitch, blade count, diameter, weight and balance—to any UAV airframe and desired flight parameters, which is exactly what they did for Stükerjürgen’s airframe. Schubeler also develops the HST EDF, often requested by universities for wind tunnel research. For instance, the DS-51HST fan/motor combo is available in a 1100kV version and 950kV version.

The Schubeler team is able to predict the performance of its fan propulsion systems in very precise flight conditions, even extreme applications. In fact, one Schubeler product is used in the stratosphere at 55,000 feet altitude.

“The future electric ducted fan propulsion systems will go in the direction of a good mix of low-speed handling, vertical climbs and jet-like speed combined with longer flying times,” Schubeler predicted.

Propelling Ahead

Schubeler and his team are also focused on a deeper dive into professional propulsion systems for commercial UAVs. “With these tough applications, we run into thermal and mechanical challenges; there is always opportunity for continuous improvement in motor design and production,” he said.

The long-term mission, Schubeler said, is to make battery-powered electric flying platforms good enough to fulfill serious enterprise missions. He pointed to the potential use of electric ducted fans as control and propulsion systems for flying machines in applications where size is limited and high static thrusts are required, for example in aerial vehicles capable of vertical take-off and landing (VTOL), hovercrafts or even actuated wingsuit flight.

Bruno Stükerjürgen and Schubeler Technologies GmbH will continue to explore electric ducted fans for high-speed aeromodelling airframes in 2020. Schubeler concluded: “Next we will develop a propulsion system that can reach 500 kph, which will take a tremendous amount of power increase for the additional 40 kph. That kind of jump won’t come from just efficiency, but we’re excited to make it happen.”

If you need efficient and reliable electric ducted fan propulsion technology, please reach out to info@schuebeler-tech.com.

This article originally appeared in Inside Unmanned Systems